DCD -- Disk Caching Disk
Disk Caching Disk (DCD) is a novel disk storage architecture
developed in HPCL for the purpose of optimizing I/O performance.
The main idea of the DCD is to use a small log disk, referred to
as cache-disk, as a secondary disk cache to optimize write performance.
While the cache-disk and the normal data disk have the same physical
properties, the access speed of the former differs dramatically
from the latter because of different data units and different
ways in which data are accessed. Our objective is to exploit
this speed difference by using the log disk as a cache to build
a reliable and smooth disk hierarchy. The log disk caches disk
writes reliably and efficiently because seek time and rotation
time are eliminated for most disk operations on the log disk.
A small RAM buffer is used to collect small write requests to
form a log which is transferred onto the cache-disk whenever the
cache-disk is idle. Because of the temporal locality that exists
in office/engineering work-load environments, the DCD system
shows write performance close to the same size RAM (i.e. solid-
state disk) for the cost of a disk. Moreover, the cache-disk
can also be implemented as a logical disk in which case a small
portion of the normal data disk is used as the log disk.
Trace-driven simulation experiments are carried out to evaluate
the performance of the proposed disk architecture. Under the
office/engineering work-load environment, the DCD shows superb
disk performance for writes as compared to existing disk systems.
Performance improvements of up to two orders of magnitude are
observed in terms of average response time for write operations.
Furthermore, DCD is very reliable and works at the device or
device driver level. As a result, it can be applied directly
to current file systems without the need of changing the
DCD is sponsored by National Science Fundation.
``Disk Caching Disk: A new device for high performance I/O system,''
U.S. Patent and Trademark Office, No. 5,754,888.
List of other publications
There is a list of other
publications and conference presentations.
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